1. Field of the Invention
The present invention relates to an ignition timing control apparatus for controlling the angle delay of the ignition timing by detecting the knocking of an internal combustion engine.
2. Description of the Prior Art
In a conventional symmetrical ignition timing control apparatus, the ignition angle is delayed upon detection of a knocking of the internal combustion engine and advanced in the absence of a knocking, thereby equalizing the amounts of angle lead and delay. In controlling the ignition timing by such an apparatus, the ratio between the frequency of detection of knockings and non-detection thereof is 1 to 1, so that the amounts of angle lead and delay are balanced out on the average. As a result, even though a small knocking (trace knocking) is detected, the knocking occurs once every two detecting operations, thereby leading to the shortcomings of a higher engine noise discordant to the driver.
A method for obviating the above-mentioned disadvantage is by an asymmetrical control in which the amount of angle delay is increased over that of angle delay to reduce the engine noise. Specifically, once a knocking is detected and the angle is delayed, the ignition timing of a predetermined number of subsequent ignitions is controlled at the set angle delay, which is advanced in the absence of subsequent knocking. If the delay angle is maintained at a fixed value for a predetermined number of ignitions in this way, however, it is impossible to promptly reduce the angle delay of ignition timing in the case where the operating condition of the internal combustion engine changes and is released from the knocking region and the knocking is eliminated.